It has been found recently in experiments that diamond/Ionsdaleite biphase could possess excellent thermal-mechanical properties,implying that the properties of carbon materials can be improved by reasonably designing their internal structures.The mechanism of the excellent performance arising from biphasic structure is still unknown and needs to be revealed.In this paper,we established a series of pos-sible diamond/lonsdaleite biphasic structures and revealed the optimization mechanism of the biphasic structure using first principles calculations.It shows in our ab-initio molecular dynamics simulations that the Ionsdaleite cannot exist stably at room temperature,which could explain why pure Ionsdaleite can hardly be found or synthesized.Detailed analysis shows that partial slip would occur in the lons-daleite region if the applied strain is sufficiently large,leading to the transition from biphasic phase to cubic phase.Then,further shear strain would be applied along the hard shear direction of the cubic structure,resulting in an ascent of stress.The results presented could offer an insight into the structural transformation at high temperature and large strain.